The present invention relates to a sheet resistance meter for measuring a sheet resistance of a thin-film metal or alloy formed on a substrate, for example, a semiconductor wafer, with a sputtering or vapor deposition technique.
Conventionally, film properties, such as thickness, composition, and size, of a thin-film metal or alloy formed on a glass substrate by a sputtering or vapor deposition technique (hereinafter, will be referred to simply as a thin-film metal) are evaluated by means of measurement of a sheet resistance of the thin-film metal. That is, the properties of a thin-film metal formed on a glass substrate are evaluated according to whether or not the sheet resistance measured falls within a predetermined range or stays below a reference value.
For this purpose, the sheet resistance may be measured, for example, through a sensor section directly contacting the thin-film metal (contact-type sheet resistance measurement technique). An example of the contact-type sheet resistance measurement technique is a four-probe scheme.
The following description will explain the evaluation of properties of a thin-film metal by a four-probe scheme in reference to FIG. 28. Note that in the four-probe scheme, the sheet resistance is not directly measured for evaluation of the properties the thin-film metal. Instead, the resistivity of the thin-film metal is measured, and the sheet resistance is obtained based on the resistivity.
First, four needle-like electrodes (probes) 203, arranged in a straight line, are placed on a thin-film metal 202 formed on a substrate 201, and a current I is applied to the two outer probes 203 to measure the potential difference V developing between the two inner probes 203 and eventually obtain the resistance (R=V/I).
Subsequently, the obtained resistance R is multiplied by the thickness t of the thin-film metal 202 and a dimensionless correction factor F determined from the shape and dimensions of the thin-film metal 202 as well as from the position of the probes 203, so as to obtain the resistivity xcfx81 of the thin-film metal 202. The sheet resistance is obtained based on the resistivity xcfx81.
In the four-probe scheme, the probes 203 are brought into contact with the thin-film metal 202 to measure the resistivity xcfx81; the thin-film metal 202 may be scratched and cause fine dust, and the probes 203 may wear out and need be changed regularly.
Further, measurement cannot be performed if the object, i.e., the thin-film metal 202 on the substrate 201, is shaking. Therefore, a dedicated attach stage needs be provided on which the substrate 201 is firmly attached. The resistivity measuring device containing such a dedicated attach stage would be inevitably bulky; therefore its accommodation in an existent manufacturing line of the thin-film metal 202 on the substrate 201 is difficult, let alone in-line measurement of the resistivity xcfx81 of the thin-film metal 202.
Another method suggested to evaluate properties of a thin-film metal is a non-contact method (non-contact-type sheet resistance measurement technique) whereby the sheet resistance of a thin-film metal is measured through metal needles or the like that do not contact the thin-film metal.
According to the non-contact-type sheet resistance measurement technique, the sheet resistance of the thin-film metal is measured by means of the eddy currents that are induced in the thin-film metal by application of high frequency electric power and lost as Joule heat.
In other words, the non-contact-type sheet resistance measurement technique makes use of the positive correlation between the conductivity and the dissipation of high frequency electric power in a thin-film metal, so as to obtain the conductivity (the reciprocal of resistivity) of a thin-film metal on a semiconductor wafer in a non-contact manner. Note that in the non-contact-type sheet resistance measurement technique, the sheet resistance of the thin-film metal is not directly measured for evaluation of the properties of the thin-film metal. Instead, the conductivity of the thin-film metal is measured, and the sheet resistance is obtained based on the conductivity.
Specifically, as shown in FIG. 29, a semiconductor wafer 301 on which a thin-film metal is formed is placed in the gap (measurement distance: 1 to 2 mm) of a ferrite core 302 around which a coil 303 connected to a high frequency generation circuit 304 is wound. Eddy currents are induced in a thin-film metal on the semiconductor wafer 301. The induced eddy currents are lost as Joule heat, and therefore the high frequency electric power is dissipated in the thin-film metal on the semiconductor wafer 301.
Hence, the high frequency electric power dissipated in the thin-film metal on the semiconductor wafer 301 is detectable as eddy current loss. The eddy current loss is transferred from the coil 303 via the high frequency generation circuit 304 to the wave detection circuit 305 and supplied as a difference in the output voltage. Then, the control circuit (not shown) obtains the conductivity of the thin-film metal on the semiconductor wafer 301 based on the output voltage from the wave detection circuit 305. Then the sheet resistance is obtained from the conductivity.
In the non-contact-type sheet resistance measurement technique, there is no sensor section directly in contact with the object, i.e., the thin-film metal: therefore, unlike in the contact-type sheet resistance measurement technique, the thin-film metal is not scratched nor does not cause fine dust, and no probes are involved that may wear out and need be changed regularly.
Incidentally, in view of control of product quality of semiconductor wafers and other glass substrates on which a thin-film metal is formed, it is preferable to measure the sheet resistance for every semiconductor wafer, etc. manufactured. To realize this, the sheet resistance should be measured for every semiconductor wafer in-line, i.e., without the semiconductor wafer leaving the manufacturing line.
In the foregoing non-contact-type sheet resistance measurement technique, as shown in FIG. 29, the ferrite core 302 is shaped so as to clamp the semiconductor wafer 301 to induce eddy currents in the thin-film metal on the semiconductor wafer 301.
Therefore, the structure of the ferrite core 302 shown in FIG. 29 renders it difficult to measure the sheet resistance on an existent manufacturing line; in order to measure the sheet resistance of the thin-film metal on a semiconductor wafer, the semiconductor wafer needs be removed from the manufacturing line to measure the sheet resistance at a different place.
Therefore, it is time-consuming to measure the sheet resistance of every semiconductor wafer, and doing so would reduce operational efficiency. For these reasons, in actual practice, one of every predetermined number of semiconductor wafers is selected for measurement of the sheet resistance, which is regarded as being equivalent in effect to the measurement of the sheet resistance of every semiconductor wafer. This holds true with the foregoing four-probe scheme.
If some semiconductor wafers are removed from the manufacturing line for measurement of the sheet resistance, and the result of the measurement shows that the sheet resistance is not normal, all the semiconductor wafers including that semiconductor wafer back to the semiconductor wafer removed last time for the measurement of the sheet resistance must be checked to see whether the sheet resistance is normal or not.
In addition, to avoid further occurrence of abnormal sheet resistance and thereby bring the sheet resistance back to a normal value, the manufacturing line must be stopped to notify a CIM process management system and a thin film forming device of the abnormal value.
Therefore, in the foregoing four-probe scheme and non-contact-type sheet resistance measurement technique, no quick action can be taken when an abnormality occurs to the sheet resistance of the semiconductor wafer in the manufacturing line. As a result, a proper management of the properties of the thin-film metal on the semiconductor wafer is impossible.
Besides, if the semiconductor wafer is constituted by a large glass substrate, a large machine is necessary to remove a semiconductor wafer from the manufacturing line and to transport the semiconductor wafer to a place where the sheet resistance is measured. This reduces operational efficiency and possibly damaging the semiconductor wafer.
These problems may be possibly solved by measuring the sheet resistance of the thin-film metal without removing the semiconductor wafer from the manufacturing line. However, the sheet resistance meter used in the foregoing non-contact-type sheet resistance measurement technique by means of eddy currents cannot be incorporated in an existent manufacturing line without modification. The sheet resistance meter can be incorporated in-line only by redesigning the manufacturing line. In such an event, the existent manufacturing line cannot be used, which adds to cost.
The present invention has an object to offer a sheet resistance meter that is readily accommodated into an existent manufacturing line so as to enable in-line measurement of the sheet resistance of a thin film and suitable control of the properties of high-resistance ITO and other thin films.
A sheet resistance meter in accordance with the present invention is a sheet resistance meter for measuring a sheet resistance of a thin film formed on a substrate, and is characterized in that it includes:
a sensor head for generating a magnetic field; and
sheet resistance detection means for, when the substrate is placed at a predetermined distance from the sensor head, detecting a variation in the magnetic field generated by the sensor head as the sheet resistance of the thin film formed on the substrate,
wherein the sensor head is disposed opposing only one of two sides of the substrate.
With the arrangement, the sensor head is disposed opposing only one of two sides of the substrate; therefore, the sheet resistance of the thin film formed on the substrate can be measured on either the top side or the bottom side, while, for example, the substrate, i.e., an object to be measured, is in the manufacturing line.
This enables the sheet resistance of the thin film formed on the substrate to be measured in a manufacturing line, and thereby, unlike conventional technology, eliminate the need to remove the substrate from the manufacturing line to measure the sheet resistance. Accordingly, the sensor head can be incorporated into an existent manufacturing process or manufacturing machine, facilitating its in-line integration.
Further, the sensor head and the substrate are placed at a predetermined distance from each other when the sheet resistance of the thin film on the substrate is measured; therefore, the sensor head can measure the sheet resistance of the thin film without contacting the thin film on the substrate.
As a result, the sheet resistance of the thin film can be measured without the sensor head scratching or damaging the substrate or the thin film formed on the substrate.
Accordingly, the sheet resistance of the thin film can be measured without the sensor head scratching the substrate or the thin film formed on the substrate.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.